As shown in FIG. 5, for example, in a single wafer processing type vapor phase growth apparatus 100 of a prior art, a semiconductor single crystal substrate (hereinafter, sometimes referred simply as a substrate) 1 is mounted on a susceptor 112 arranged in a reaction chamber, the substrate 1 is rotated almost horizontally with the susceptor 112, gas is introduced into the reaction chamber 102 from one side (for example, the left side in FIG. 5) along a direction of an arrow A and is exhausted to other side opposite to the introduction side along a direction of an arrow B, the substrate 1 is heated to a desired temperature setting by using a heating apparatus (not shown) installed outside of the reaction chamber 102, and a semiconductor single crystal thin film (hereinafter, sometimes referred simply as a thin film) is grown by a vapor phase growth method on a front surface of the substrate 1.
Because conditions such as temperature (especially the temperature of the substrate 1), temperature distribution (especially the temperature distribution within the surface of the substrate 1) and the like influence properties of the thin film during the vapor phase growth, proper control of these conditions are essential.
Control of the temperature and the temperature distribution is performed, for example, by feeding back detected temperatures of a substrate 1 (for example, heated by halogen lamps) by thermocouples to a heat output of the heating apparatus and by heating the substrate 1 so as to make the detected temperatures of the substrate 1 approach to setting temperatures.
The thermocouples are respectively located in a plurality of regions of the reaction chamber such as a central region of the substrate, a side surface region, a gas introduction region and a gas exhaust region and the like. Temperature of each region is detected by the corresponding thermocouple, and the temperatures of the regions are independently controlled according to the detected temperatures by using, for example, the halogen lamps.
The thermocouples are installed in a heat retaining plate 115 arranged so as to surround the susceptor 112. In detail, thermocouples 101a, 101b, 101c and 101d are installed in the heat retaining plate 115 so as to place, for example, one thermocouple 101d at the position corresponding to the center of the substrate 1 and place three thermocouples 101a (the side surface region of the reaction chamber), 101b (the gas exhaust region) and 101c (the gas introduction region) at the peripheral positions of the substrate 1, and temperature at each position is detected.
Temperature change with the passage of time, which is detected by the thermocouple located at each of the positions of the reaction chamber 102 (the center of the substrate, the gas introduction region and the gas exhaust region), is shown in FIG. 6. As shown in FIG. 6, the temperature detected in a gas introduction region R100 (shaded area in FIG. 5) by the thermocouple 101c is higher than the temperatures detected in both the center of the substrate 1 and the gas exhaust region by the thermocouple 101d and the thermocouple 101b respectively.
The gas introduction region R100 in the reaction chamber 102 is cooled down due to the gas introduced at almost room temperature. Therefore, assuming that the output power for heating is uniformly set in the whole area in the reaction chamber 102, the periphery temperature of the substrate at the gas introduction region becomes low as compared with temperatures in the other area of the substrate 1. As a result, slip dislocation undesirably and easily occurs.
Accordingly, to prevent the slip dislocation occurring due to the reason described above, temperature setting in the gas introduction region R100 is relatively heightened. Therefore, as described above, temperature detected in the gas introduction region R100 becomes higher than those detected at the center of the substrate and the gas exhaust region.
Incidence of the slip dislocation depends on temperature setting difference between two points on a surface of a substrate 1 (unit of ° C.), that is, an offset level of the temperature setting. Therefore, it is preferable to set the offset level so as to lower the incidence of the slip dislocation as possible.
On the other hand, resistivity distribution in a growing thin film changes in accordance with the offset level of the temperature setting. FIG. 4 is a graph showing a correlation between the offset level of the temperature setting (X-axis) and the resistivity distribution (Y-axis; resistivity difference between the center and a periphery of the substrate) of the thin film.
This graph is obtained by changing the offset level of the temperature setting at the gas exhaust region against that at the center of the substrate and by growing a silicon single crystal thin film having a thickness of about 7 μm and a resistivity of about 10 Ω·cm by a vapor phase growth method at a temperature of 1110° C. on a front surface of a p+-type silicon single crystal substrate to which boron is added at high concentration.
The X-axis indicates differences between setting temperatures of heating for the center of the substrate and setting temperatures of heating for the gas exhaust region, during thin film formation. Temperature at the center of the substrate is detected by the thermocouple 101d, and temperature in the gas exhaust region is detected by the thermocouple 101b. The Y-axis indicates a value (unit of Ω·cm) obtained by subtracting an average of resistivity values at four peripheral positions from a resistivity value at the center of the thin film in a grown silicon single crystal thin film. As the value of the Y-axis approaches to zero, uniformity of in-plane resistivity distribution is heightened.
A range of the offset level in which no slip dislocation occurred in the growth conditions described above is shown in FIG. 4 as a range H100. That is, when the offset level is within a range of −60° C. to −70° C., slip dislocation scarcely occurs. However, slip dislocation easily occurs in out of this range H100.
According to FIG. 4, to make in-plane resistivity distribution be substantially 0 (zero), setting the offset level to be −95° C., that is, setting the temperature at the gas exhaust region lower than the temperature at the center of the substrate by 95° C. is required. However, when the temperature setting difference between the gas exhaust region and the center of the substrate is so large as described above, the offset level becomes out of the range H100, and slip dislocation occurs easily.
Contrarily, to make slip dislocation scarcely occur, because the least offset value is −70° C. (within the range H100), when a silicon single crystal thin film with resistivity of about 10 Ω·cm is grown by a vapor phase growth method, lowest resistivity difference between the center and a periphery in the thin film can be at most 0.7 Ω·cm or so.
Each detected temperature denotes a temperature detected by a thermocouple and is slightly different from actual temperature of the substrate 1.
In order to solve the above problem, an object of the present invention is to provide a vapor phase growth method and a vapor phase growth apparatus which can improve in-plane resistivity distribution while suppressing occurrence of slip dislocation.